In optical communication systems, the need exists for a variety of coupling devices where light signals can be switched among various transmission elements. For example, 1.times.2 and non-blocking 2.times.2 optical switches can be used in a variety of networking applications. In ring networks, the requirement is to be able to have a node (e.g., a host computer) either participate in the network or be bypassed. This bypass function is required so that a particular node is decoupled from the network in the event of a malfunction. Bypass is also used for self testing before a node connects to the network. More specifically, in the bypass condition the node needs to be able to have its transmitter talk to its own receiver to verify that it is operating correctly before being reconnected to the network. This condition is termed local loopback.
At least one proposal has been made for a multiport coupler using a graded index of refraction (GRIN) lens. In U.S. Pat. No. 4,304,460, issued to Tanaka, et. al., an array of fibers is coupled to one surface of the lens and a rotatably mounted mirror is provided at the other surface. Incoming light is diverted from one fiber to another by means of rotating the mirror. While adequate, the need for a motor to rotate the element adds complexity and cost to the coupler and may decrease reliability under prolonged use in the field. An alternate proposal was made by Levinson in U.S. Pat. No. 4,626,066, where the rotating mirror was replaced by a cantilevered arm etched into a piece of silicon. The micromachined cantilevered mirror appears attractive for ease of manufacturing but the part may be difficult to align to the fiber array on the other end of the GRIN lens and hence may result in inferior performance.
It is the object of the present invention to provide a compact, low cost 2.times.2 non-blocking switch which can channel light among various transmission elements in a controlled manner.